1. Technical Field
The present invention relates to switching mechanisms applicable to cameras. More particularly, the present invention relates to a structurally simple, low-noise, and low wear-and-tear mechanism for switching the filters of a camera without using complex control and feedback units.
2. Description of Related Art
For a general camera equipped with a CCD or CMOS sensing element to maintain a satisfactory image-capturing state in the daytime as well as at night, it is necessary to switch filters for diurnal and nocturnal use of the camera respectively so that high image fidelity is achieved in the daytime, and clear pictures can be taken during the nighttime. Therefore, filter-switching mechanisms are commonly provided in cameras.
A variety of filter-switching mechanisms are now available on the market. These mechanisms can be divided, by the control methods involved, into the following two types.
The “closed-circuit control mechanisms” are the most basic and popular automatic switching mechanisms. In such a mechanism, be it used in a mechanical, electronic, or optical device, sensors are provided at a starting point and a terminal point of the switching operation so as to detect the object being switched and feed back electronic signals to a control chip, which then actuates or stops a driving device (usually a motor) accordingly, thereby realizing the desired switching function. When the object driven by the motor reaches a predetermined position or condition, a signal is fed back to the control chip so as to adjust the operation of the motor. While this control method monitors the conditions of the object being switched and provides reliable control over the object, it is nevertheless disadvantaged by high costs and bulky design.
On the other hand, in an “open-circuit control mechanism”, an input unit provides one-way positive control over a motor so that the motor drives an object without detecting its conditions. Mechanisms of this type are advantageously simple and economical because no special controllers and feedback mechanisms are required. However, since there are no position sensing devices (e.g., switches and sensors) for detecting the conditions of the driven object, once the object is blocked from moving but the driving device (e.g., a motor) is not timely stopped, components along the driving link, such as the motor or a transmission mechanism (most probably the motor), will be damaged. Therefore, in order to protect the components, it is necessary to incorporate into the control mechanism a mechanism for making and breaking the connection between the driven object and the driving device. One of the most popular solutions involves providing control by frictional constraint. While this friction-based solution is mechanically simple and economical, it has such inherent and unconquerable defects as blindness toward the conditions of the driven object and significant operational noise.
Thus, there is a need for a novel switching mechanism that is applicable to cameras and capable of eliminating all the above problems.